People skilled in the art recognize the goal to mass produce a solenoid actuator having smaller initial and final air gaps with improved parallelism between a stator assembly and an armature in a cost efficient manner. Even though it may be possible to produce a solenoid actuator assembly having a very small air gap and where the armature is parallel to the stator assembly, those in the art recognize there are significant costs involved in mass producing such assemblies.
Typical solenoid actuated fuel injectors include an armature connected to a valve member that controls the flow of fuel and/or pressure through the fuel injector. By having the armature connected to the valve member, the movement of the armature within the stator assembly may be compromised. By moving the armature with the valve member coupled thereto, the armature might travel at reduced speeds due to the increased mass, and any attempts to improve parallelism with the stator assembly were also hindered due to the tolerance stack ups that invariably increase during production with more connected parts. Moreover, in the past, some armature assemblies included a hard guide piece that was part of, or drove a fuel injection valve member, and a soft armature piece that served to enhance the magnetic forces acting on the armature. In order to improve parallelism and maintain a predetermined initial and final air gap, manufacturers used various category parts that took into account the inaccuracies that existed in the dimensions of the solenoid actuator assembly despite establishing very tight tolerances during mass production.
When the coil of the solenoid is energized, the armature moves towards the stator assembly, moving the valve member, and thereby controlling the fluid flow and/or pressure in the fuel injector. When the coil ceases to be energized, a mechanical spring or other bias forces the armature away from the stator assembly, causing the valve member to return to its original position and thereby controlling the fluid flow and/or pressure in the fuel injector again. It is known in the art that the time taken for the solenoid actuator, and hence the control valve of a fuel injector, to move from a first position to a second position and back again is a function of the highest possible forces acting on the armature over the shortest possible travel distance. It is desired by those in the art to reduce the time taken for the armature to travel from the initial air gap position to the final air gap position and back to the initial air gap position.
The magnetic forces acting on the armature are functions of the electromagnetic properties of the armature, the initial and final air gap between the armature and the stator assembly and the parallel orientation of the armature with reference to the stator assembly, including others. It is well known in the art that a magnetic field in a solenoid has the greatest force when the armature is parallel to the stator assembly and the air gap between them is as small as possible. Having a larger initial air gap will translate to the armature having a lower initial attraction force and maybe a larger travel distance, hence increasing the time taken to travel from the initial air gap position to the final air gap position. Having a smaller final air gap will allow for a smaller initial air gap and also allow a stronger magnetic force to act on the armature, hence increasing the speed at which the armature travels from the final air gap position to the initial air gap position and back. A lack of parallelism can create side forces leading to imbalance and increased wear at guide interfaces.
There has been an ongoing effort to improve parallelism in prior references, while striving to achieve the smallest final air gap. One prior art reference, U.S. Patent Application US2006/0138374 A1 teaches the use of an adjustable spacer coupled between the armature housing and the stator. The spacer is adjusted depending on the tolerance variation of the assembled parts. U.S. Pat. No. 6,550,699 teaches the use of plating a hard film layer on the armature as a spacer. The prior art, although geared towards achieving some of the goals this disclosure aims to achieve, have been met with limited success.
The present disclosure is directed to one or more of the problems set forth above.